Microcrystalline cellulose (MCC) is a white, odorless, tasteless, relatively free flowing, crystalline powder that is virtually free from organic and inorganic contaminants. It is a purified, partially depolymerized cellulose obtained by subjecting alpha cellulose obtained as a pulp from fibrous plant material to hydrolytic degradation typically with mineral acid. It is a highly crystalline particulate cellulose consisting primarily of crystalline aggregates which are obtained by removing amorphous (fibrous cellulose) regions of a cellulosic material. MCC is used in a variety of applications including foods, pharmaceuticals and cosmetics.
Microcrystalline cellulose may be produced by treating a source of cellulose, preferably alpha cellulose in the form of pulp from fibrous plant materials, with a mineral acid, preferably hydrochloric acid. The acid selectively attacks the less ordered regions of the cellulose polymer chain thereby exposing and freeing the crystalline sites which form crystallite aggregates which constitute the microcrystalline cellulose. These are then separated from the reaction mixture, and washed to remove degraded by-products. The resulting wet mass, generally containing 40 to 60 percent moisture, is referred to in the art by several names, including hydrolyzed cellulose, hydrolyzed cellulose wetcake, level-off DP cellulose, microcrystalline cellulose wetcake or simply wetcake.
When the wetcake is dried and freed of water the resulting product, microcrystalline cellulose, is a white, odorless, tasteless, relatively free-flowing powder, insoluble in water, organic solvents, dilute alkalis and acids. For a description of microcrystalline cellulose and its manufacture see U.S. Pat. No. 2,978,446. The patent describes its use as a pharmaceutical excipient, particularly as a binder, disintegrant, flow aid, and/or filler for preparation of compressed pharmaceutical tablets.
Microcrystalline cellulose and/or hydrolyzed cellulose wetcake has been modified for other uses, notably for use as a gelling agent for food products, a thickener for food products, a fat substitute and/or non-caloric filler for various food products, as a suspension stabilizer and/or texturizer for food products, and as an emulsion stabilizer and suspending agent in pharmaceutical and cosmetic lotions and creams. Modification for such uses is carried out by subjecting micro-crystalline cellulose or wetcake to intense attrition forces as a result of which the crystallites are substantially subdivided to produce finely divided particles. However, as particle size is diminished, the individual particles tend to agglomerate or hornify upon drying, probably due to hydrogen or other bonding forces between the smaller sized particles. To prevent agglomeration or hornification, a protective colloid, such as sodium carboxy-methylcellulose (CMC), which wholly or partially neutralizes the bonding forces which cause agglomeration or hornification, may be added during attrition or following attrition but before drying. This additive also facilitates re-dispersion of the material following drying. The resulting material is frequently referred to as attrited microcrystalline cellulose or colloidal microcrystalline cellulose. For a description of colloidal microcrystalline cellulose, its manufacture and uses, see U.S. Pat. No. 3,539,365.
Colloidal microcrystalline cellulose is a white odorless, hygroscopic powder. On being dispersed in water, it forms white, opaque thixotropic gels with microcrystalline cellulose particles less than 1 micron in size. It is manufactured and sold by FMC Corporation (FMC) in various grades under the designations, among others, Avicel RC and Avicel CL, which comprise co-processed microcrystalline cellulose and carboxymethylcellulose sodium.
Recognizing the unacceptability of CMC in food ingredients in certain well-populated countries, McGinley in U.S. Pat. No. 4,263,334 avoids the use of CMC in a colloidal microcrystalline cellulose by using a combination of additives consisting of a first ingredient which is a carbohydrate sweetner, e.g., sucrose, dextrose, or hydrolyzed cereal solids, and a second ingredient which is a hydrocolloid, e.g., guar gum, locust bean gum, gum arabic, sodium alginate, propylene glycol alginate, carrageenan, gum karaya, or xanthan gum.
Another MCC-based stabilizing agent is described by Tuason et al. in U.S. Pat. No. 5,366,742. This agent is prepared by mixing colloidal MCC with sodium alginate in water and then adding a soluble calcium salt to the slurry in an amount which deposits a sodium, calcium alginate complex on the surface of the MCC to provide barrier coating properties. After homogenization, the slurry is spray dried. The resulting stabilizing agent may be redispersed in water by use of high shear methods which appear to break the calcium alginate crosslinks, thus allowing dispersion to occur. However, in order to disperse this stabilizing agent using minimal agitation, it is necessary to provide a calcium sequestrant to preferentially react with the calcium in the sodium, calcium complex, thereby solubilizing the alginate.
Not all hydrocolloids when coprocessed with MCC in accordance with prior art processes provide effective barrier coating properties to the spray-dried powder that is produced. In U.S. Pat. No. 5,192,569 McGinley et al. describe the coprocessing of MCC and a galactomannan gum, e.g., locust bean or guar gum. Prior to spray drying, the MCC is attrited and is, therefore, colloidal. However, the flocculated product is claimed to be comprised of spherical particles ranging in size from 0.1 to 100 microns. In Example 1 for instance, spray dried powder has a particle size range of 5-70 microns. Reconstitution or rehydration of this coprocessed material requires high shear conditions. In compositions having 15 weight % or more of the galactomannan gum, high shear dispersion of the spray-dried material results in fibrous particles. Either the spherical aggregates or the fibrous material is particularly effective in providing fat-like properties to foodstuffs.
U.S. Pat. No. 6,391,368 (Tuason et al.) discloses a composition comprising attrited colloidal microcrystalline wetcake which is coprocessed with iota carrageenan and dried. The composition is prepared by the following process:
(a) subjecting hydrolyzed cellulose alone to attrition to make colloidal microcrystalline cellulose;
(b) dispersing said colloidal microcrystalline cellulose in water heated to a temperature above the solubility temperature of the dry iota carrageenan to be coprocessed with said colloidal microcrystalline cellulose;
(c) adding the dry iota carrageenan to the heated dispersion of colloidal microcrystalline cellulose and mixing the components, creating a slurry;
(d) homogenizing said slurry; and
(e) drying said slurry to produce a coprocessed powder.
U.S. Pat. No. 6,037,380 (Venables et al) discloses a composition comprising microcrystalline cellulose, a relatively water insoluble attriting aid and, optionally a protective colloid. The compositions are prepared by the following process:
(a) blending together unattrited microcrystalline cellulose, an attriting agent which is relatively insoluble in water and optionally a protective colloid;
(b) subjecting the blend to high shear wet grinding for a time and under shear forces sufficient to reduce the particle size of the microcrystalline cellulose, and
(c) recovering the resulting ultra fine microcrystalline cellulose composition.
U.S. Pat. No. 6,117,474 (Kamada et al.) discloses a composition containing a fine cellulose and a water-insoluble calcium material. The compositions are prepared by cogrinding an aqueous suspension of cellulose particles and calcium particles. A water soluble gum and/or hydrophilic substance may be incorporated in order to prevent re-aggregation of the fine cellulose and water-insoluble calcium material upon drying.
U.S. Pat. No. 6,270,830 (Kamada et al.) discloses a stabilizer for meat products comprising fine cellulose and a gelling agent. The stabilizer may contain a potassium or calcium salt such as insoluble calcium carbonate, to control gelling.